1. Field of Invention
The present invention relates generally to the field of wireless communication and data networks. More particularly, in one exemplary aspect, the present invention is directed to methods and apparatus for managing a heavy influx of radio network access attempts (such as those generated by a plurality of self-managing user devices accessing a cellular network within a brief period of time), so as to manage the processing burden on the network.
2. Description of Related Technology
Modern wireless networks which are adapted to serve large geographic areas generally comprise a plurality of fixed transceivers (e.g., base stations) in order to communicate with the plurality of user devices (e.g., mobile telephones or computers). One such system is the well known cellular telephone system, which employs numerous individual and unique coverage areas or “cells” which collectively form a cohesive patchwork or network for coverage of the desired geographic area. Subsets of these cells, such as those in close geographic proximity to one another, or which have another common physical or logical relationship to one another, may be bundled together to form integrated entities for purposes of operation of the network. Common cellular systems in use today include those compliant with the 3G (e.g., UMTS) or GSM standards.
Universal Mobile Telecommunications System (UMTS) is an exemplary implementation of a “third-generation” or “3G” cellular telephone technology. The UMTS standard is specified by a collaborative body referred to as the 3rd Generation Partnership Project (3GPP). The 3GPP has adopted UMTS as a 3G cellular radio system targeted for inter alia European markets, in response to requirements set forth by the International Telecommunications Union (ITU). The ITU standardizes and regulates international radio and telecommunications. Enhancements to UMTS will support future evolution to fourth generation (4G) technology
In the exemplary context of a UMTS system, a base station is commonly referred to as a “NodeB”. The UMTS Terrestrial Radio Access Network (UTRAN) is the collective body of NodeBs along with the UMTS Radio Network Controllers (RNC). The user interfaces to the UTRAN via User Equipment (UE), which in many typical usage cases is a cellular phone or smartphone. FIG. 1 illustrates an exemplary UMTS cellular system 100. The UMTS system comprises a plurality of base station towers 102 (NodeBs) that are set at various fixed geographic locations. Each of these base station towers is characterized by their respective wireless coverage areas 104. Within UMTS, groupings of base stations are further divided into Location Areas 108 (LA) and Routing Areas 106 (RA) based on geographical proximity. The Core Network 110 generally governs the operation of the base stations, LAs, and RAs. Subscriber operated user equipment (UE) in the coverage area of one base station, may move to another base station coverage area, handling call setup and operation overhead transparent to the user.
Relay stations or repeaters (not shown) may be used in certain areas within the network, such as those with a high density of users (e.g., in train tunnels, etc.), in order to improve the signal coverage in such areas. Normally, such relay stations merely amplify the upstream or downstream radio signals. These relay stations are typically fixed, but may themselves also be mobile or at least portable (i.e., capable of migration and setup at different locations).
Within a UMTS network, one of the aforementioned “integrated entities” comprises an LA 108 (FIG. 1), which is defined as a wireless coverage range for a circuit-switched (CS) network, serviced by one or more base stations 102, in which a UE may move freely without updating its current location at the Visitor Location Register (VLR), a component to be described in greater detail below. When a UE moves outside its LA, it informs the VLR of its current location through a location update procedure. Each Location Area is uniquely identified across all Public Land Mobile Networks (PLMN) by the Location Area Identity (LAI) which comprises a Mobile Country Code (MCC), Mobile Network Code (MNC), and Location Area Code (LAC).
Similarly, an RA 106 is defined as a wireless coverage range for a packet-switched (PS) network, serviced by one or more base stations 102, in which an UE may move freely without updating its current location at the Serving GPRS (General Packet Radio Service) Support Node (SGSN). An RA is functionally similar to an LA, other than the differences related to CS/PS, and corresponding network structures (VLR, SGSN). An additional difference between RA and LA is that an RA is always contained within an LA. This dependency is reflected in the Routing Area Identity (functionally similar to the LAI), as the RAI a concatenation of the LAI with an addition of a Routing Area Code (RAC).
LA and RA tracking for UEs enable efficient Mobility Management (MM) within a UMTS cellular network. MM is necessary for the network to deliver calls, SMS and other mobile phone services. If the LA(s)/RA(s) are large, there will be many mobile devices operating simultaneously, resulting in very high paging traffic, as every paging request has to be broadcast to every base station 102 in the LA/RA. This wastes bandwidth and power on the UE, as the UE must listen for paging traffic constantly. If there are too many small LA(s)/RA(s), the UE must contact the network frequently to update location changes, which will also drain the UE's battery. Therefore, a balance must be struck between a larger LA/RA which increases network overhead during paging, and a smaller LA/RA which increases the frequency of LA/RA updates. The design tradeoff between paging area and frequency of paging also dictates the size disparity between LA and RA; although the “bursty”, high data rate usage of PS data (handled with RAs) is more efficiently handled with a smaller paging area, CS data (handled with LAs) is more efficiently handled with larger area.
As previously mentioned, the UE must inform the cellular network whenever it moves from one location area to the next. The location area update procedure (which is functionally similar to the routing area update procedure) allows a UE to inform the Core Network 110, whenever it moves from one location area to another, so that the Core Network may page the UE in its new area. Mobiles are responsible for detecting the broadcast LAC/RAC. When a mobile finds that the LAC/RAC is different from its last update, it notifies the network with a message comprising an update request, with its previous location, and it's Temporary Mobile Subscriber Identity (TMSI), or in some cases its International Mobile Subscriber Identity (IMSI) which is a unique network identifier.
FIG. 1A, illustrates the foregoing issues by way of an exemplary platform (passenger train 150) with a large UE 152 spatial density (e.g. 3000-4500 people) crossing an LA/RA boundary. As the train crosses the LA/RA boundary, each unconnected UE (a UE not already maintaining a data connection to the network) initiates a LA/RA update.
Initiating a Radio Link, RACH/AICH Operation
FIG. 2 shows the processing of PRACH preambles 200 of the establishment of a radio link. As depicted, the UEs 152 are transmitting on a Physical Random Access Channel (PRACH) 252. The NodeB is transmitting on the physical Acquisition Indication Channel (AICH) 254.
FIG. 2A illustrates the format of the Random Access Channel (RACH), which is a transport channel mapped onto the Physical Random Access Channel (PRACH) 252. The RACH encapsulates, inter alia, the Common Control Channel (CCCH). The CCCH may include requests to set up radio resource control (RRC) connections, and dedicated control information. The RACH may also be used for sending some dedicated user information, and small amounts of uplink packet data. As shown in FIG. 2A the PRACH uplink signal may be formatted into data 210 or control 212 (preambles are not shown, as they contain no messaging information) accesses. Each PRACH has 15 time slots 214 (2560 chips in length). A radio frame 216 is 15 time slots.
FIG. 2B further illustrates the random access transmission 218 capability of the RACH. The RACH has 15 access slots 220. Each access slot consists of two 10 ms time slots 214. Per two 10 ms radio frames 216 (20 ms), there are 15 possible RACH access slots.
FIG. 2C illustrates the format of the AICH 254, which is a common control channel broadcasted by the NodeB 102. The AICH carries an acquisition indication that is 32 symbols in length 222, corresponding to a received PRACH 252 preamble. The AICH is dedicated for transmission of acquisition indications, and does not have any other messaging format. As with the PRACH, the AICH has 15 access slots 220 per two radio frames (20 ms).
The AICH 254 and PRACH 252 channels as shown in FIG. 2A and FIG. 2B have only 15 separate access slots within a 20 ms window. Furthermore, the timing of AICH responses to PRACH preambles is fixed. Therefore, a limited number of preambles and corresponding RACH accesses may be served in any particular time interval.
Referring back to FIG. 2, exemplary PRACH 252 and AICH 254 traffic is illustrated. Initially, a UE (UE#A 152A) must determine system timing of the NodeB 102 by demodulating broadcast control channel information. UE#A calculates the initial RACH transmission power based on the Common Pilot Channel (CPICH) signal strength of the new cell. UE#A chooses a time slot 214 out of a set of available time slots, and a signature out of a set of 16 available orthogonal signatures. UE#A sends at the chosen time slot a fixed preamble coded with the chosen signature 202A. The initial power is calculated as described above, and expected to be too low to be received by the base station. When UE#A does not receive a AICH response, UE#A increases transmit power of the preamble. The preamble is escalated until either the NodeB signals on the AICH, or the UE reaches its maximum allowed preamble transmit power.
Once the NodeB 102 receives a preamble 202A correctly, the NodeB can determine UE#A's 152A uplink propagation delay, and aligns its AICH 254 accordingly. The acquisition indication (or ACK) 204A is transmitted with the received signature on the AICH.
UE#A 152A receives and demodulates the AICH 254, thereafter, and then verifies that the ACK 204A encapsulates the expected signature. If UE#A determines that the AICH was correctly received, it corrects for NodeB propagation delay, and sets its own transmit power at the corresponding preamble transmit power. UE#A transmits corresponding RRC connection request on the RACH 206A using corrected transmit power, and timing.
Due to the high possibility of contention over the PRACH 252, the NodeB 102 may signal a NACK 208BC. This is illustrated when a second UE (UE#B 152B) and third UE (UE#C 152C) transmit preambles 202B, and 202C respectively. The NodeB receives both preambles, and determines that a collision has occurred. The NodeB signals a NACK 208BC. UE#B and UE#C both desist from further preamble transmission, and back off for a randomized period of time. At a later point, UE#B initiates a preamble access 202D, and is acknowledged correctly by the NodeB with a corresponding ACK 204D. Once a previously idle UE has established a radio link, the UE may proceed with the RA update.
Location Area/Routing Area Entities
FIG. 3 is a simplified system diagram illustrating the entities involved in a typical LA/RA update process. LA and RA update processes are fundamentally similar (with some exceptions due to CS/PS, as previously explained).
The Core Network 110 (see FIG. 1) consists of a CS domain, and a PS domain. Each domain has corresponding entities which perform similar functions and are simultaneously connected to the same UE, but which remain distinct from one another. The Core Network CS domain is comprised of Mobile Switching Centers (MSCs) and Visitor Location Registers (VLRs). The PS domain is comprised of Serving GPRS Support Nodes (SGSNs) 306 and Gateway GPRS Support Nodes (GGSNs) 310. The MSC/VLRs 304 manages CS data (e.g. voice calls, SMS, etc.), SGSNs manages PS data (e.g. IMS access, etc.), each within their respective geographic locations.
Access, and authorization control is governed primarily by the Home Location Register/Authentication Center (HLR/AuC) 302, which acts a central database that can uniquely identify and verify each subscriber that is authorized to use the Core Network. Once a UE has authenticated itself with the HLR/AuC, the UE's identity is transferred to the corresponding MSC/VLRs 304 and SGSNs 306.
Packet Data access to external networks is governed by the Gateway GPRS Support Node (GGSN) 310; the GGSN is the network entity that acts as a gateway between a GPRS wireless data network and other networks (e.g. the Internet, private networks, etc.). Among other functions, the GGSN provides requested external network access to the Serving GPRS Support Node (SGSN) 306 by converting data from GPRS data packets (i.e. SGSN format), to the external network protocol (e.g. TCP-IP).
The Radio Access Network (RAN) 308 is comprised of Radio Network Controllers (RNCs) and base stations (NodeBs). Each RNC manages a plurality of NodeBs 102. As previously mentioned, NodeBs are grouped into LAs 108, and may be further subdivided into RAs 106. The RAN manages the radio bearing elements to support CS and PS traffic. The Core Network 110 is not involved in radio resource allocation.
Exemplary Routing Area Update
Referring now to FIG. 3A and FIG. 3B, the entities involved in an RA update process are shown interacting during a typical update process.
In FIG. 3A, the UE 152 detects the presence of an additional base station 102B. It reads the system information broadcasted by the base station and determines that the new base station belongs to the same PLMN, but is in a different RA 106B than that to which the UE is currently allocated. The UE performs measurements to gain information about the signal strength. The new base station's signal strength is higher than the threshold for a cell update. If the UE has an RRC connection, it will perform an RA update using the existing connection to optimize the data routing (FIG. 3B).
A UE 152 in idle mode cannot immediately perform an RA cell update, because the UE is not connected to either the old SGSN 306B or the new SGSN 306A. In order to correctly update the Core Network 110 with the new RA 106B, the UE must establish a new RRC connection. Establishment of the RRC connection requires initiation of a radio link.
The RA update procedure for UMTS systems is based on GSM mobility management procedures, as shown in FIG. 4A. The entities' Mobile Station (MS) and Base Station Subsystem (BSS) are synonymous with UE 152 and NodeB 102 respectively. The evolution in terminology originated with the change from GSM to GPRS to UMTS (2G to 2.5G to 3G networks).
The MS 152 is responsible for detecting RACs that are broadcast from the base stations 102. When an MS finds that the RAC is different from its last stored RAC, it performs an update by sending a Routing Area Update Request 402, together with its previous location, and Temporary Mobile Subscriber Identity (TMSI).
The Mobility Management Entity (MME) within the SGSN 306 identifies the user with the use of the encrypted TMSI. Under certain conditions, (e.g., if the user has not been authenticated), the MME will require an authentication and key agreement (AKA) to complete successfully 404. After the UE 152 and MME have completed the AKA, and mutual authentication has completed, the MME updates the Home Location Register 302 (HLR), and initiates local security activation procedures. After the UE has completed local security integrity and encryption procedures, the SGSN sends a Routing Area Update Accept 406. The MS confirms receipt and setup with a Routing Area Update Complete message 408.
As shown in FIG. 4B, when the MS 152 sends the Routing Area Update Request 402 to the SGSN 306, the MS also starts a timer T3330, and changes to state GMM-ROUTING-AREA-UPDATING-INITIATED. The BSS adds the Cell Global Identity, including the RAC and LAC of the cell where the message was received, before passing the message to the SGSN 306. Security functions may also be executed 404. After any such security procedures are completed, the SGSN validates the MS′ presence in the new RA 106B. If, due to regional subscription restrictions, the MS is not permitted to be attached in the RA, or if subscription checking fails, the SGSN rejects the Routing Area Update with an appropriate cause 408. To limit the number of subsequently rejected Routing Area Update attempts, a Routing Area Updating attempt counter is introduced. Depending on the value of the Routing Area Updating attempt counter, specific actions are performed. The Routing Area Updating attempt counter is reset when a Routing Area Updating procedure is successfully completed, when the MS is in sub-state ATTEMPTING-TO-UPDATE and a new RA is entered, the timer T3302 has expired, or the registration function requests termination. A Routing Area Update Rejection 408 carries a code which identifies the cause of rejection; these codes are shown in FIG. 4C. Upon reception of certain cause codes, such as #96, 99, or #111 (shown in FIG. 4C), or #95 (semantically incorrect message) or #97 (message type non-existent or not implemented), not shown in FIG. 4C, the MS 152 will set the Routing Area Updating attempt counter to a value of five (5). If the procedure is restarted four times, then on the fifth expiry of timer T3330, the MS will abort the procedure. If the Routing Area Update procedure fails a maximum allowable number of times, or if the SGSN 306 returns a Routing Area Update Reject message, the MS will remain in the IDLE state.
If all checks are successful, the SGSN 306 updates the MM context for the MS 152, and a Routing Area Update Accept 406 message is sent to the MS. A Routing Area Update Complete 408 message is returned to the network only if the Routing Area Update Accept 406 message contained a new P-TMSI or a request for the provision of the Inter RAT information container.
A limitation of the prior art location update procedure occurs when the number of UEs 152 initiating location updates exceeds network capabilities. In the previously discussed example illustrated in FIG. 1A, as the passenger train crosses the LA/RA boundary, the sudden influx of simultaneous registration traffic exceeds typical network traffic, creating an overload of network resources as the number of simultaneous random accesses lead to collisions, and subsequent multiple attempts (a “cascade” effect of sorts, since each collision breeds at least two subsequent attempts). In an extreme case (e.g. Tokyo rush hour) this network overflow could occur as often as once every few minutes or more.
Several solutions have been contemplated in the prior art which relate to multiple Location Area/Routing Area updates. For example, U.S. Pat. No. 6,556,820 to Le, et al. issued Apr. 29, 2003 and entitled “Mobility management for terminals with multiple subscriptions” discloses a scheme for providing mobility management for terminals with multiple subscriptions. The invention integrates Europe's Universal Mobile Telecommunications Standard (UMTS) subscriber identity module-specific procedures into single procedures, and which uses a common TMSI. An UMTS subscriber identity module is allocated for each subscription associated with a mobile terminal, wherein each UMTS subscriber identity module being identified by an identification code. A location area update is performed by providing a single location area update request message comprising a list of identification codes for each UMTS subscriber identity module associated with the mobile terminal. Each USIM is authenticated separately, and some USIMs may fail, while others may succeed authentication. The terminal and network each build their own Ordered List of Registered USIM-IDs (OLRU) which records the USIMs that succeeded. The network assigns a Base TMSI, which is similar to the current assignment of TMSIs. Subsequent Location Area Update procedures use the Base TMSI, which is common to all USIMs in the OLRU. Thus it does not have to be repeated for each USIM. Paging Request uses the Base TMSI, along with a USIM Specifier (USIMS) field, which specifies which USIM(s) is being paged. USIMS is kept very compact with bit string coding, which also gives flexibility to page multiple USIMs at the same time. The terminal and network interpret the bit string by using the OLRU. The terminal has to listen to only one paging subchannel. The paging subchannel is determined by calculating the sum modulo N of the last digits of the USIM-IDs in the OLRU. N is the number of possible subchannels.
U.S. Pat. No. 6,968,190 to Suumaki, et al. issued Nov. 22, 2005 and entitled “Transfer of optimization algorithm parameters during handover of a mobile station between radio network subsystems” discloses a method whereby instead of renegotiating parameters relating to an optimization algorithm previously negotiated between a mobile station and a target radio network subsystem during connection handover of the mobile station from a source radio network subsystem, prestored parameters are transferred instead between the source radio network subsystem and the target radio network subsystem either directly over an existing Iur interface or via a core network over an Iur interface.
U.S. Pat. No. 6,968,196 to Back, et al. issued Nov. 22, 2005 entitled “Location area update in a communication system” discloses a method and a controller for a radio communication system. The system comprises a plurality of location areas. The controller serves said location areas and mobile stations within said location areas. In accordance with the method a request for initiation of location area information update proceedings is received at the controller. The controller then verifies whether the mobile station is subjected to a simultaneous paging procedure. If a simultaneous paging procedure is detected, the location area information update proceedings are interrupted and an acknowledgement message is generated and transmitted, said message informing the mobile station that the location area information update proceedings are completed.
U.S. Pat. No. 7,181,212 to Hogan, et al. issued Feb. 20, 2007 and entitled “Method and apparatus for location area updating in cellular communications” discloses a radio access network that provides information to a mobile radio terminal indicating a list of one or more geographic coverage areas from which the mobile radio terminal may or may not obtain service. In the preferred example embodiment, a “forbidden” list includes one or more geographic coverage areas from which the mobile radio terminal may not obtain service. The mobile checks the received information when considering whether to request service from a new geographic coverage area, and determines whether to select the geographic coverage area depending on that received information. Moreover, the mobile terminal consults that list to determine whether to perform a location area update procedure. In other words, if the list indicates that a new geographic coverage area should not be selected, the mobile terminal does not perform a location area update request in that new coverage area.
U.S. Pat. No. 7,333,795 to Dorsey, et al. issued Feb. 19, 2008 and entitled “Emergency call placement method” discloses an emergency call placement method used in user equipment in idle mode camped on a first cell of a wireless communication network having a first radio access technology includes the steps of requesting a radio resource control connection using “emergency call” as an establishment request, changing to a new cell in a different location area or routing area than the first cell, and requesting again a radio resource control connection using “emergency call” as an establishment request. This method avoids performing a location area update or a routing area update when the user equipment changes to a new cell during an emergency call and thus may speed up placement of the emergency call by several seconds.
U.S. Pat. No. 7,333,811 to Liu issued Feb. 19, 2008 and entitled “Method and apparatus for utilizing historical network information for mitigating excessive network updates when selecting a communications channel” discloses a method and apparatus for utilizing historical network information for mitigating excessive network updates when performing channel selection between a serving base transceiver station and an adjacent base transceiver station when determined channel selection would result in either a Location Area Update (LAU) or a Routing Area Update (RAU). If a network update, either LAU or RAU, is the first occurrence, network identification information for the LA or RA is stored and an incremental value indicating occurrence is set; else in the case occurrence is not the first, the incremental value is incremented. A first margin value is then selected if the incremented value does not meet or exceed a predetermined value, or a second margin value is selected if the incremented value does meet or exceed a predetermined value. The signal level of the adjacent base transceiver station is then compared to the reference signal level of the serving base transceiver station plus the selected margin value in order to determine channel selection.
United States Patent Publication No. 20060133347 to Das published Jun. 22, 2006 and entitled “Integrating mobility agents for short messaging services” discloses a method of providing messaging services for GSM or 3G mobile stations. A gateway detects a mobile network registration from a mobile station, and performs a location area update procedure with previous support nodes from its home public land mobile network. The gateway then receives data for the mobile station from a packet switched radio network and transmits the data for the mobile station through the mobile network.
Great Britain Patent Publication No. GB2367454 to Cheung, et al entitled “Location area and routing area update signalling in a cellular communications system” discloses A method for Combined Location Area, (LA)/Routing Area (RA) Update message signaling in GPRS and UMTS cellular communications systems that utilizes a Combined Update RA/LA message containing information of new Location Area Identity (LAI), International Mobile Station Identity (IMSI), Serving GPRS Service Node (SGSN) Number, Location Update Type, and new VLR; and an Insert Subscriber Data message 1d containing information of new LAI, IMSI, SGSN Number; and Location Update Type. This produces a signaling procedure which allows the Combined LA/RA Update to occur in parallel, and reduces the number of signaling messages required. Additionally, an Insert Subscriber Data Acknowledge message may contain information of VLR TMSI (Temporary Mobile Station Identity), allowing another message to be saved.
U.S. Pat. No. 6,937,868 to Himmel, et al. issued Aug. 30, 2005 and entitled “Apparatus and method for managing a mobile phone answering mode and outgoing message based on a location of the mobile phone” discloses an apparatus and method for managing a mobile phone answering mode and outgoing message or other indicator based on a location of the mobile phone. The apparatus and method make use of a location system to ascertain the current location of a mobile telephone being carried by a user. Based on the current location, the apparatus and method determine whether operation of the mobile telephone to receive and/or send calls should be restricted. In addition, the apparatus and method determine an appropriate outgoing message to be provided to calling parties while the mobile telephone is located in an area where use of the mobile telephone to receive calls is prohibited. The particular outgoing message provided is customized to the current location of the mobile telephone and optionally, the caller ID of the calling party.
U.S. Patent Publication No. US2007213057 to Shaheen entitled “Method And Apparatus For Supporting Routing Area Update Procedures In A Single Tunnel GPRS-Based Wireless Communication System” discloses a method and apparatus for supporting routing area update procedures in a single tunnel general packet radio services (GPRS)-based wireless communication system are disclosed. A wireless transmit/receive unit (WTRU) sends a routing area update request message to a serving general packet radio service (GPRS) support node (SGSN) via a radio network controller (RNC). The SGSN sends an update packet data protocol (PDP) context request message to a gateway GPRS support node (GGSN). The GGSN sends an update PDP context response message to the SGSN. The SGSN sends a tunnel establishment request message to the RNC and a single tunnel is established between the RNC and the GGSN. For handover operations, a previous single tunnel established between the GGSN and another RNC is released and the routing area update is accepted and completed.
WIPO Publication No. WO9930524 to Monrad, et al entitled “Method For Routing Area (RA) Update” discloses a method for routing area (RA) update request messages which in accordance with a time period broadcasted from the network are periodically sent from an MS (Mobile Station) to an SGSN (Serving GPRS Support Node) through a BSS (Base Station System), which SGSN supports GPRS (General Packet Radio Service), and which as a result of a routing area update procedure will return an appropriate accept message, and for the purpose of taking into account the differentiation in nature of normal routing area update procedure and periodic updates, it is according to the present invention suggested that for the purpose of simplifying said routing area update procedure, there is broadcasted a new indicator from the network together with the time period for the periodic routing updates, said indicator being adapted to determine whether the periodic routing update procedure is performed ciphered instead of unciphered.
Despite the foregoing variety of approaches, the prior art fails to provide an adequate solution for mitigating a sudden influx of simultaneous registration attempts within a wireless network, such as in the exemplary UMTS context previously described. Accordingly, a solution is needed which promptly and effectively manages (e.g., preemptively diffuses) a plurality of access or update attempts by a plurality of UEs concurrently initiating location updates when transitioning from one LA/RA to another LA/RA.
Ideally, such improved methods and apparatus would be transparent to the user, so as to maintain a high level of “user experience” and avoid interruptions and loss of service. They would also be consistent with and even leverage existing wireless infrastructure, network policies, and functional capabilities, and would minimally impact the software and hardware apparatus of both the client devices and base stations involved (including having a minimal or no impact on power (e.g., battery charge) consumption.